The present application is directed to electronic ballasts. It finds particular application in conjunction with the resonant inverter circuits that operate one or more fluorescent lamps and will be described with the particular reference thereto. However, it is to be appreciated that the following is also amenable to high intensity discharge (HID) lamps and the like.
A ballast is an electrical device which is used to provide power to a load, such as an electrical lamp, and to regulate the current provided to the load. The ballast provides high voltage to start a lamp by ionizing sufficient plasma (vapor) for the arc to be sustained and to grow. Once the arc is established, the ballast allows the lamp to continue to operate by providing proper controlled current flow to the lamp.
Typically, after the alternating current (AC) voltage from the power source is rectified and appropriately conditioned, the inverter converts the DC voltage to AC. The inverter typically includes a pair of serially connected switches, such as MOSFETs which are controlled by the drive gate control circuitry to be “ON” or “OFF”.
One approach to operate multiple fluorescent lamps connected in parallel is to use a design similar to driving a single lamp, where each lamp is operated by a dedicated inverter, e.g. n lamps require n inverters. However, this approach is costly.
The following contemplates new methods and apparatuses that overcome the above referenced problems and others.